It has been desired for many years to reduce the noise impinging upon individuals at home, at work, and in the multitude of other places in which people find themselves. In addition to regulations under the Federal Occupational Safety and Health Act to reduce noise levels in the workplace, certain municipalities are changing building codes, adopting stricter standards and imposing new specifications for party walls and interior floor/ceiling assemblies between apartments.
For many years increasing the mass density of a wall was considered as being the only way to improve the sound attenuation characteristic of structures. It was then found that separating the two halves of the wall construction produced a slight degree of sound reduction and filling the cavity between the two halves with a low density soundwave-absorbing membrane such as mineral wool further increased the sound reduction. A further increase in the reduction of sounds in structures was realized when it was found that thermoplastic foams when constructed in certain forms have a degree of sound resistance and inhibit to some extent the transmission of noise from one area to an adjacent area. However, it is also known that current thermoplastic foam constructions are subject to resonant short-comings which create areas where substantial loss of sound attenuation occurs throughout a broad frequency spectrum.
A recent development which has found some acceptance for floor/ceiling noise attenuation is a space filling mat of widely-spaced, three-dimensional, nylon non-woven matting covered on one face by a fabric. An example of this construction is the Enkasonic.TM. matting produced by American Enka Company.
Foamed thermoplastic laminates have also been used in automobiles, particularly in the headliners. These foamed thermoplastic laminates are most often formed with the foamed thermoplastic material enclosed between outer facings. An example of this construction is the Fome-Cor.RTM. board produced by Monsanto Company which is a polystyrene foam which has a kraft liner board facing on each side. The Fome-Cor.RTM. board would be prepared for use by die-cutting and scoring or by pressing the board and applying a resin to fix the pressed shape. In an alternative construction a styrene-maleic anhydride foam sheet is covered with a thermoplastic polymer skin. A decorative trim was often applied to the automotive interior side of the headliner. This decorative trim has typically been a thin layer of polyurethane foam covered with cloth or vinyl.